"Emanuele Colucci" wrote in message
...
Thank you John for this message.
J. Mc Laughlin ha scritto:
You are commended for initiative in wishing to have a radio
telescope. Crafting such an instrument can be an end into itself.
However, having an observational goal seems to be desirable if this is
more than a construction project. I recommend that you read the ample
literature that is available to help you design an observational goal.
Yep, I'm still documenting. Perhaps, there are alternatives to a Cas
antenna (Yes, I admit, because of exams I haven't crafted it yet, but for
me this is a very long term project), like a little array of offset
parabolic antennas.
Note that you need a large size if you are to achieve resolution,
which might not be an objective. I worked on the receiving system for a
system at NRAO at Green Bank, W.Va. that used a fixed, high gain antenna
to observe (once a day) the strength of one source. The antenna used had
a predictable gain and, with calibration, the system was able to provide
flux measurements (with an attendant uncertainty, of course).
This is interesting!
How much time did it take to make a complete radio stellar map?
Note that the first real radio telescope by Reber was a parabolic dish -
it still exists. (He was a really bright, innovative guy.)
Reber's parabolic dish is giant 
My site is situated in countryside, and
it could be able to host dishes of max 3 meters of diameter: the data
would be transmitted over the internet to my home (near Naples, ITA).
The presence of antennas used to receive satellite broadcasts that
use offset feeds should be considered. Such antennas can have desirable
antenna temperatures because of the placement of the feed while not
having feed-blockage.
Great. I'll watch for these antennas too!
Most important is the avoidance of re-inventing the wheel that can be
effected by serious study of the literature. That is where I recommend
that you start. Kraus' books on antennas and radio-astronomy could be a
good place to start. It would be wonderful to be young and have so much
learning to look forward to! After over 50 years of studying radio
related subjects, I am still excited.
Thanks again for reporting your experiences and the advices!
I haven't read Kraus book about radio astronomy: my sources are Collin and
some italian books by Flavio Falcinelli. But now I'll surely look for this
book too!
Greetings,
Emanuele Colucci
Hi Emanuele
The probability of your realizing any success with parabolas less then 10
feet diameter using cassegrain systems is extremely low at L-band. I
realize that you are able to decide for yourself, which antenna system is
best for your project. I do want to alert you to the fact that the beam
from the "source radiator", behind the dish, needs to be shaped to be
concentrated on the reflector at the focus. There is not enough room in a
3 meter dish to provide access to a primary feed with the narrow beam
required for realizing the benefits of a cassegrain feed.
I have has some succes with a 1 meter off center fed dish at L-band (1.691
GHz) for redceiving signals from a geosynchronouis satellite. The feed I
designed for that dish might be of some use to you.
Jerry KD6JDJ